As known, a SIM is so small that it is attached to a plastic support when it is released from a factory. The SIM and the respective plastic support are also referred to as SIM module. The consumer of the SIM buys the SIM module and detaches the SIM from the plastic support, for usage. For facilitating the detachment, the SIM is attached to the plastic support by one or more precut lines.
FIG. 1A schematically shows a SIM module with punching holes and precut lines. A card body 110 includes a SIM 115, a mini SIM or micro SIM. Two punch holes 120, 125 on the left and right side of the SIM 115 and two pre-cut lines 130, 135 on top and bottom side of the SIM 115 are provided for facilitating its detachment from the plastic support of the SIM module. FIG. 1B and FIG. 1C schematically show the manufacturing process of the SIM module. The SIM 115 is formed on the plastic support of the module 110 as one part. Then, the target cutting boundary S1, S2 are made, based on the plastic support size and the SIM size and the respective position. The area is usually pre-calculated and it can be corrected based on the error of the manufacturing process.
A portion of the left and right side of the SIM module are removed by a punching process as depicted in FIG. 1C. After the punching process, left hole 125 and right hole 120 are formed just near the SIM 115. In this state, the target cutting boundary S1, S2 still remains on top and bottom side of the SIM 115. The target cutting boundary S1, S2 needs to be processed to form on the top and bottom sides of the SIM 115 pre-cut lines.
FIG. 2A shows the cross section of the blades used at the pre-cut process. Top blade 200 and bottom blade 210 enter the plastic support 110 and form the pre-cut lines moving along the target cutting boundary. In FIG. 2A, the top blade 200 and the bottom blade 210 are arranged symmetrically based on the central plane 110 of the support.
Due to the symmetry of the blades, the final product with the pre-cut line can obtain reliability and easily detachable characteristics. However, a precise symmetry can be obtained in an exceptionally ideal situation. In the real manufacturing process, there is asymmetry on the top blade 200 and the bottom blade 210, caused by undesirable and unpredictable circumstances.
FIGS. 2B, 2C, and 2D schematically illustrate examples showing the asymmetry occurring on the top and bottom blades. In FIG. 2B, the bottom blade 210 penetrates the central plane 220, which causes a deeper bottom pre-cut line on the full-sized card 110. In FIG. 2C, the top blade 200 penetrates the central plane 220, which causes a deeper top pre-cut line on the full-sized card 110. In FIG. 2D, the top blade 200 and the bottom blade 210 are not aligned in a line, which causes top pre-cut line and bottom pre-cut line to be formed asymmetrically in a different position. These kinds of errors happen frequently and are difficult to detect.
Moreover, the asymmetrical pre-cut lines cause overbalanced stress distribution on the SIM 115 and local bending. The bending introduces stress localized on the micro-module of the SIM and causes problems during card transport on the next process. In an extreme case where a pre-cut line is absent or is formed ineffectively, it may cause damage during the plug-in detach.
Other technical problems may be associated with the pre-cut line area. More particularly, the manufacturing process requires two process steps, which is more costly. The blade penetration is a mechanical process, and thus the production is frequently impacted from the blade stopping in it's rail, due to the powder or loss of lubrication. Furthermore, it is not easy to detect the asymmetrical pre-cut line before doing a destructive mechanical test. Continuous changing of blades, rail cleaning, and fine tuning adjustments may increase the production cost.
French patent No. 2806661 suggested a SIM having three linking pieces which are connected to the plastic support. Two of the three linking pieces are disposed on one side of the SIM and the other is disposed on the opposite side of the SIM card. The two linking pieces are disposed symmetrically on the other opposite side's linking piece. Although it is not drawn clearly in the FIG. 2, the linking pieces of the bottom side each have a pre-cut, to let the SIM be detached from the plastic support.
Moreover, since the SIM comprises three linking pieces, one of which is arranged in the opposite side from the other two linking pieces, the consumer should apply a strong force to break at least one of the linking pieces at first.